Glaucoma is an ocular disorder wherein the intraocular pressure of the eye is elevated so as to cause damage to the optic nerve. This produces loss of visual field. Unless treated, the disease may gradually progress to complete blindness. Nature and causes of the disease are discussed generally in Cecil Textbook of Medicine, (15th Ed. 1979) at p. 2322 et seq. It has been estimated that 2-3% of all people over 40 years of age have glaucoma.
Primary open-angle glaucoma occurs predominantly in people over forty years of age and is the most common form of all glaucomas. In virtually all open-angle glaucomas, elevated intraocular pressure is caused by an increased resistance to outflow which results from changes in the trabecular meshwork, Schlemm's canal, or adjacent efferent channels. Open-angle glaucomas are usually treated medically by the administration of drops. When unsuccessful, medical treatment is followed by laser and/or surgical treatment.
The cause of open-angle glaucoma has been theorized as arising from an imbalance between the extraocular muscles and the longitudinal fibers of the ciliary muscle in W. Kamerling, et al., "The Role Of The Extraocular Muscles In Open-Angle Glaucoma", Glaucoma, Vol. 1, No. 1 (February 1979). The suggested treatment was to weaken the extraocular muscles so as to restore balance between the extraocular muscles and the ciliary muscle.
With age, there is a gradual sclerosis and weakening of the ciliary muscle. The muscle becomes atrophic and hyalinized. The ciliary muscle may be divided into three groups of fibers: longitudinal, radial and circular. Contraction of the longitudinal ciliary fibers opens the trabecular spaces through which the aqueous fluid of the eye exits. As the longitudinal fibers of the ciliary muscle weaken, the trabecular spaces remain narrow resulting in an increased resistance to aqueous outflow and, eventually, open angle glaucoma.
Presbyopia is a condition wherein the ability of the lens to focus on near objects becomes more difficult. The lens is connected by fibers, known as zonules, to the ciliary body of the eye. Contraction of the circular fibers of the ciliary muscle relaxes the zonules and permits the lens to widen, i.e., increase in size in its anterior-posterior diameter, and thus focus more clearly on near objects. As the circular fibers of the ciliary muscle weaken, there is a decrease in the ability of the lens to change shape and to focus on near objects resulting in presbyopia.
Electrical stimulation of the extraocular muscles (occular recti) of the eye has been proposed to treat strabismus in U.S. Pat. No. 4,271,841 titled "Electro-ocular Stimulation System" issued June 9, 1981 to Harry G. Friedman incorporated herein by reference. The patent discloses a body implantable unit including an electrode implanted over or in the extraocular muscle. The electrode is coupled by a lead to a portion of the implantable unit which develops the stimulation signal. The purpose of the stimulation signal is to trigger contraction of the agonistic extraocular muscle.
It is an object of the present invention to provide repeated, controlled electrical stimulation of the ciliary muscle to increase aqueous outflow through the trabecular meshwork and reduce intraocular pressure and thereby prevent or treat open angle glaucoma.
It is a further object of the invention to provide such stimulation to allow the lens of the eye to widen and focus on near objects and thereby prevent or treat presbyopia.